1. Field of the Invention
The present invention relates to optical testing devices for measuring the quality of image resolution from a given test surface. In particular, the present invention is designed for measuring the image resolution of aspheric mirror surfaces.
2. Description of the Prior Art
Previous optical surface test fixtures relied on indirect measurement of the quality of the image produced. The standard testing device was the Zygo interferometer, Fizeau type. The Zygo interferometer, in addition to its time consuming evaluation of a split beam monochromatic light interference pattern reflected off of the test surface, provides a surface figure measurement and does not produce an actual measurement of the blur circle size.
In addition to interferometric techniques, the quality of the test surface has frequently been measured by measuring the amount of normal incident scattered light to random scattered light to determine the percentage of light maintained within the beam. Again, this does not provide a precise measurement of the size of the blur circle. This technique measures mirror quality rather than mirror figure. In general, aspheric surfaces have not been used in optical devices because they have been hard to fabricate and, once fabricated, it is hard to measure the image quality with any degree of certainty.